Heat sink



FIG. 1 is a perspective view of a heat sink showing our new design;

FIG. 2 is a right side view thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a left side view thereof; and,

FIG. 7 is a rear view thereof. 

The ornamental design for a heat sink, as shown and described herein. 